The present invention relates to a liquid crystal device for use in a liquid crystal display device, an optical shutter array, etc., and more particularly to a liquid crystal device having improved display and driving characteristics, because of improved initial alignment or orientation of liquid crystal molecules.
Hitherto, there have been well known liquid crystal devices using TN (twisted nematic) type liquid crystal as shown, for example, in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. In this type of liquid crystal device, the number of picture elements has been restricted, because there is a problem that a crosstalk phenomenon occurs when a device of a matrix electrode structure with a high density of picture elements is driven according to a time-sharing or time-division driving scheme.
As another type of liquid crystal device, there has been known one comprising a plurality of picture elements each connected to and subject to switching by a thin film transistor as a switching element. This type of liquid crystal device, however, is accompanied with problems such that production of thin film transistors on a substrate is very complicated, and production of a display device with a large picture area or screen is difficult.
In order to obviate the above-mentioned draw-backs of the conventional types of liquid crystal devices, Clark and Lagerwall have proposed the use of a liquid crystal device using a bistable liquid crystal (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Pat. No. 4367924, etc.). The bistable liquid crystal to be used may be a ferroelectric liquid crystal having a chiral smectic C (SmC*) phase or another phase such as chiral smectic H (SmH*) phase, chiral smectic F (SmF*) phase, chiral smectic I (SmI*) phase or chiral smectic G (SmG*) phase.
Such a ferroelectric liquid crystal has bistability, i.e., has two stable states comprising a first stable state and a second stable state. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the second stable state in response to the other electric field vector. Further, this type of liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficulties involved in the conventional TN-type liquid crystal device. This point will be explained hereinafter in further detail in connection with the present invention.
However, in order that an optical modulation device using the liquid crystal having bistability could show desired operation performances, the liquid crystal interposed between a pair of parallel base plates is required to be placed in such a state of molecular arrangement that the transition between the two stable states can effectively occur, as a matter different from, or a precondition of, the application of an electric field. With respect to, for example, a ferroelectric liquid crystal having an SmC* or other phases, there must be formed a monodomain wherein the layers of the liquid crystal molecules are perpendicular to the face of the base plate and therefore the axes of the liquid crystal molecules are almost in parallel with the base plate face. However, in the optical modulation devices using a bistable liquid crystal, and orientation or alignment state of a liquid crystal having such a monodomain structure cannot satisfactorily be formed, whereby the optical modulation device cannot actually show sufficient performances.
For example, several methods have been proposed to give such an orientation state, including a method of applying a magnetic field and a method of applying a shearing force. These methods have not necessarily provided satisfactory results. For example, the method of applying a magnetic field requires a large size of apparatus and is not readily compatible with a thin layer cell which is generally excellent in operation performances. On the other hand, the method of applying a shearing force is not compatible with a process where a cell structure is first formed and then a liquid crystal is poured thereinto.